(i) Field of the Invention
The present invention relates to a compound useful as a light-absorbing agent which can play an important role in optoelectronics fields of information recording, display sensors and protective spectacles, and it also relates to an optical recording medium such as an optical disc or optical card in which the above-mentioned compound is contained in a recording layer.
(ii) Description of the Related Art
Semiconductor laser beams are utilized for writing and reading of data in and from devices such as optical discs and optical cards. Particularly, as a recording system of optical recording media which are used in these devices, heat mode recording (thermal recording) which involves light/heat exchange is usually employed at a practical level. Therefore, as materials for a recording layer, there have been suggested low-melting metals, organic polymers, and organic dyestuffs which give rise to a physical change or chemical change such as melting, evaporation, decomposition or sublimation. Above all, the organic dyestuffs having a low melting point or decomposition temperature are preferable in point of recording sensitivity, and therefore cyanine dyestuffs, phthalocyanine dyestuffs, naphthalocyanine dyestuffs and azo dyestuffs have mainly been developed as the materials of the recording layer.
For example, in Japanese Patent Application Laid-open No. 147286/1990, an optical recording medium in which a cyanine dyestuff is contained in the recording layer has been suggested. However, this type of medium is poor in long-term shelf stability and light resistance, and recording properties are also insufficient.
Optical recording media containing an anthraquinone dyestuff (e.g., Japanese Patent Application Laid-open No. 224448/1983) and a naphthoquinone dyestuff (e.g., Japanese Patent Application Laid-open No. 224793/1983) in recording layers have also been suggested. However, they are poor in long-term shelf stability and light resistance, and recording properties are also insufficient, as in the cyanine dyestuffs.
In Japanese Patent Application Laid-open Nos. 25886/1986, 43269/1990 (U.S. Pat. No. 4,960,538) and 296885/1990, optical recording media containing naphthalocyanine dye-stuffs in recording layers have been suggested. These media are excellent in light resistance, but reflectance and recording properties of the recording layers are insufficient.
Furthermore, techniques for utilizing phthalocyanine dyestuffs, particularly alkoxy-substituted phthalocyanines in recording layers of optical recording media are well known as disclosed in Japanese Patent Application Laid-open Nos. 154888/1986 (EP 186404), 197280/1986, 246091/1986, 39286/1987 (U.S. Pat. No.4,769,307), 37991/1988 and 39388/1988. It cannot be considered that the optical recording media using the phthalocyanine dyestuffs which are disclosed in these patents have satisfactory sensitivity and recording properties. The improvement of these media has been suggested in Japanese Patent Application Laid-open No. 62878/1991 (U.S. Pat. No. 5,124,067), but even said advanced media disclosed therein have still insufficient recording property for making an especially high-speed and high-density recording.
There have been suggested applications, to optical recording media, of alkoxy-substituted phthalocyanines in Japanese Patent Application Laid-open Nos. 43269/1990 (U.S. Pat. No. 4,960,538) and 296885/1990, aliphatic hydrocarbonoxy-substituted phthalocyanines in Japanese Patent Application Laid-open No. 37991/1988, and alkenylthio-substituted phthalocyanines in Japanese Patent Application Laid-open No. 39388/1988. However, in "Detailed Description of the Invention" and "Examples" of these inventions, neither an unsaturated hydrocarbon-oxy nor -thio group containing a double bond is described. Needless to say, it is not described anywhere that the unsaturated hydrocarbonoxy group containing a triple bond or double bond between carbons is effective for sensitivity and recording properties of the optical recording medium.
Among the optical recording media in which other known dyestuffs are used, the media which are sufficiently excellent in performance such as recording properties have not been found so far.
In writing and reading data in and from the optical recording media, a laser beam of 400-900 nm is utilized, and therefore it is important to control an absorption coefficient, a refractive index and the like of the recording material in the vicinity of the oscillation wavelength of the used laser beam, and it is also important to form precise pits in writing and reading. They are particularly important for high-speed recording and high-density recording which are desired in recent years. For the reason, it is necessary to develop a dyestuff for the optical recording media having a high structure stability, a high refractive index to light in the vicinity of oscillation wavelength of the laser beam, good decomposition properties and high sensitivity. However, the conventionally developed dyestuffs for the optical recording media have problems that they are poor in sensitivity (a C/N ratio and an optimum recording power) and recording properties (jitter and deviation) particularly at the times of high-speed recording and high-density recording.